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| A newbie needs some help with my first DSO |
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| awakephd:
--- Quote from: tautech on May 31, 2024, 10:54:07 am --- --- Quote from: awakephd on May 30, 2024, 02:06:03 pm ---To take a practical example, if I am trying to decode some messages on an SPI bus, here is what I think I am understanding: On the Siglent, I will need to show "all" of the messages on the screen to capture them - even though at that point they will be so squished together than I can't discern the content of any of the messages. Then, once capture, I can zoom in and scroll through to see the actual content of the messages. Have I got it right? --- End quote --- To a point. Ideally we always want to see a truly stable waveform which signifies trigger settings are correct at least for basic decoding. While there are several shortcuts to get a result my advice to get accustomed to the absolute power of the trigger suite you have. Some KISS examples using a single channel for UART. To get a properly stable waveform you need to prevent retriggering within a packet using a Holdoff time setting a little longer than a packet. How long is a packet is the first thing we need to know and for this we need get a few packets on the display and press Stop and eyeball its width against the graticules. For these examples a 60ms Holdoff is just adequate to get rock solid stable triggering. However, while we are still in the trigger menu, we need set the correct edge which for most protocols is Idle High so we need a falling edge trigger to mark the beginning of packet data. Now we should have sound triggering however with the H Pos mid display there's only half the display to show full packets and their decode so we need move H Pos to the left with the encoder and set it in place with Utility/System Settings/Ref Position with H Pos set to Position. The back of the job is now broken and just decode settings remain, assigning the correct channel/s and Threshold levels, Idle High in this case, baud rate etc. As has been discussed Zoom mode can be useful now to display a # of packets to permit panning through them and the zoomed window for each packet decode or each byte. Hoping the attached screenshots are of assistance. --- End quote --- I was able to follow some of that ... will have to sit down and try actually to decode a signal in order to see if I truly understood or not. Unfortunately, this weekend is tied up with a trip, so it may be a few days before I get time. :( |
| tggzzz:
--- Quote from: awakephd on May 31, 2024, 04:57:36 pm ---I was able to follow some of that ... will have to sit down and try actually to decode a signal in order to see if I truly understood or not. Unfortunately, this weekend is tied up with a trip, so it may be a few days before I get time. :( --- End quote --- Can I suggest starting with a signal you know, either: * a "simple" standard like a square wave with 0.1% duty cycle and sharp edges * a complex serial stream like a program "printing" A...Za...z to a UART, with/without spaces between the characters |
| awakephd:
--- Quote from: tggzzz on May 31, 2024, 05:33:04 pm ---Can I suggest starting with a signal you know, either: * a "simple" standard like a square wave with 0.1% duty cycle and sharp edges * a complex serial stream like a program "printing" A...Za...z to a UART, with/without spaces between the characters --- End quote --- Oh, believe me, I am starting simple. Last night I set up an ATTiny84 to output 0 - 254 on 8 of its pins - nice, simple square waves of varying frequencies to test, try out the various available measurements, etc. I even did an FFT, not that I truly know enough about FFTs to understand how to set it up or what I was seeing as a result ... |
| tggzzz:
--- Quote from: awakephd on May 31, 2024, 10:53:42 pm --- --- Quote from: tggzzz on May 31, 2024, 05:33:04 pm ---Can I suggest starting with a signal you know, either: * a "simple" standard like a square wave with 0.1% duty cycle and sharp edges * a complex serial stream like a program "printing" A...Za...z to a UART, with/without spaces between the characters --- End quote --- Oh, believe me, I am starting simple. Last night I set up an ATTiny84 to output 0 - 254 on 8 of its pins - nice, simple square waves of varying frequencies to test, try out the various available measurements, etc. I even did an FFT, not that I truly know enough about FFTs to understand how to set it up or what I was seeing as a result ... --- End quote --- FFT of digital signals... The square wave's period shows up in the frequency domain as the fundamental frequency plus odd harmonics. The highest harmonic is determined by the transition time; the period is irrelevant. Varying the duty cycle changes the amplitude of the low frequency harmonics, but the high frequency harmonics are unaffected. Maybe https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/ might help a little by confirming the theory you will learn. But learning how to trigger on characters emitted by a UART is a useful way of understanding your scope's capabilities. Doubly so when comparing it with a logic or protocol analyser. |
| OLderDan:
--- Quote from: tggzzz on May 31, 2024, 11:11:34 pm --- ...But learning how to trigger on characters emitted by a UART is a useful way of understanding your scope's capabilities. Doubly so when comparing it with a logic or protocol analyser. --- End quote --- First I want to thank OP for starting such an interesting thread, but, I get here and the story just stops? |
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